This invention relates to fish feed, and more particularly but not exclusively, to an improved composite fish feed for use in feeding cultured fish in aquatic farms and the like.
In any environment where fish or similar aquatic creatures are bred in captivity, it is obviously necessary to provide them with a balanced diet containing all of the nutrients which would be available to them in the wild, so as to ensure that healthy fish are reared.
There are many different types of feed available. For example, International Patent Application No. WO02/24000 describes feed pellets consisting of wheat, fish meal and maize gluten in various quantities. However, there are a number of issues to be considered in connection with fish feed of this type, including the sustainability of the ingredients, the provision of a balanced diet, and the preservation of the water quality over a period of time.
Polychetes have been used as part of a maturation diet for shrimp for over 15 years. These have generally been used fresh or fresh/frozen and have either been fed with other fresh or fresh/frozen materials such as Squid and Artemia or blended with dry materials immediately before feeding.
More recently polychetes have been used as part of a maturation diet for other species such as pelagic and demersal fish, being fed in a similar way to shrimp maturation diets. Polychetes represent an ingredient source that has extremely high levels of palatability as well as contributing a so-called “factor X” that brings species to sexual maturity.
International Patent Application WO02/00035 A1 describes a bioactive food complex product for use in aquaculture of shellfish and finfish. It is stated herein that aquaculture of shellfish and finfish provides high-value food products for human consumption and has been the most rapidly growing sector in international agribusiness. It is further stated that continued progress in aquaculture is limited by (a) the lack of adequate commercial feeds during critical hatchery and nursery phases, and (b) the devastating losses to disease in all production phases, particularly in shrimp farming. It goes on to say that hatchery and nursery operations typically depend on supplies of fresh and live food organisms, including polychete worms to produce aquaculture seedstock for grow-out and production aquafarms. However, because these foods are collected from the wild, they typically carry high bacterial loads. Thus, the use of fresh and live food organisms (collected from the wild) increases the risk of disease in the hatchery and these disease agents can be transported to nursery and grow-out facilities via the seedstock. This problem is addressed in WO02/00035 by providing a bioactive food complex including selected probiotics incorporated within the feed to assist in controlling bacterial diseases in aquaculture.
However, a further problem, which is not addressed in WO02/00035, is that the nutritional value of the wild, fresh food organisms which can be used in the type of bioactive food complex described is variable and is, in many cases, very low, depending on the environment from which they are collected. Some may, for example, have lived in an environment in which they were exposed to toxins; others may have had a shortage of nutritional sustenance. Thus, there is no consistency in the nutritional value of the resultant feed.
In summary there are a number of good reasons why fresh ingredients such as polychetes should be processed into Ready for Use feeds rather than taken to the hatchery as raw creatures, as listed below:                1. Variability in performance caused by Variability of Fresh Ingredients;        2. Variability in performance caused by poorly controlled blending/feeding;        3. Lack of Consistency of Supply;        4. Water Quality Problems;        5. Perceived or Real Risks of Spread of Disease;        6. Limitations to Use.        
Looking at these issues in turn, if polychetes or other fresh materials are sourced by using indigenous supplies there can be variability in quality of the materials caused by poor control of harvesting. These wild caught materials are not controlled in a cultivated environment and are subject to seasonal, nutritional and life cycle changes. As an example small immature polychetes have a very different lipid profile to more mature animals. Wild caught animals are not likely to be put through a cleaning cycle at point of harvest to allow the intestine to empty and contamination with other species is likely, especially if for instance a dredging operation is used to catch them.
These same issues arise wherever a wild species is harvested without any attempt being made to control the cultivation of the species. Another and perhaps more serious issue is the potential for contamination of the fresh caught material from one of the many man-made toxins that we send down our rivers into the seas of the world. The potential issues with fishmeal are well known and these issues if anything can be more serious when harvesting estuarine creatures if the total environment they are growing in is not understood. Picture 2 shows a typical European beach from which wild polychetes are dug.
The answer to this is to sustain the population of the fresh ingredient by cultivation techniques, which for the marine polychete means growing the animal in land-based ponds, where careful control of feeding, water quality, time of harvesting and preparation between harvesting and processing are all able to be controlled carefully. With other fresh marine ingredient sources it is equally important to understand and control source of supply.
When putting together a typical shrimp maturation feed the operator is asked to take the fresh materials and chop them into a size suitable for feeding to the shrimp. Note that if the polychetes or other fresh ingredients are in frozen form they may contain a variable amount of moisture, depending on how they have been frozen. If they have been allowed to thaw or if unknown freeze/thaw cycles have occurred there may have been deterioration in the material before the operator gets hold if it.
The various fresh ingredients are chopped and fed in cycles, the uneaten remains being cleaned out of the tanks after a while. This gives the target species the opportunity to selectively feed, eating more of one of the fresh ingredients than the others. Use of only fresh ingredients also means there is no opportunity to supplement the feed with micro nutritional ingredients, thus limiting the end user in terms of feed formulation. Picture 4 of bag of frozen polychetes.
Finally, the end user depends when feeding fresh ingredients on a high level of skill at the point of feeding, the operator having to be consistent in the selection, preparation and feeding of the fresh ingredients. This is difficult enough when feeding species such as shrimp, but is even more difficult when maturing fish species and much more difficult with starter feed.
Currently, many fresh ingredients such as polychetes are harvested using an independent chain of individuals who supplement their income by going down to the beach and digging. This has resulted in apparently cheap costs for these materials, the cost being no more than the price a person expects for their labour. The real cost of this is now being realised, when the beaches that were the source of this abundant harvest are drying out. As in so many other areas where we harvest without replacement the earth is running out of yet another resource.
Feeding fresh materials can affect the quality of the water in the feeding tanks due to leaching from the feed into the water. Interstitial fluids from the fresh materials certainly leaches very quickly into the water where cells have been damaged during the cutting and preparation of the fresh materials for feeding. For this reason it is better if the fresh ingredients could be packaged in a way that would minimise leaching of these materials. Processing into an encapsulated, pelleted or flaked form can be carried out to achieve this.
If fresh ingredients are taken from the marine environment immediately adjacent to the fish or shrimp farms then fed back as maturation or brood stock feed there is a significant risk that any diseases will keep going round the loop, recontaminating new generations before they get anywhere near grow-out ponds or nets. In this circumstance there is a need to first carefully screen the wet ingredients for disease then, if necessary, ensure the fresh ingredients pass through a process which kills or inactivated the disease vector.
If the wet ingredients are taken from a location remote from the fish or shrimp farm the probability of disease transmission is reduced. If, to take it a stage further, the fresh ingredients come from a “cold water” northern climate and are used to feed “warm water” species in locations extremely remote from the source of the wet ingredients, the probability of disease transmission is almost eliminated. It is still important to monitor the fresh ingredients, pass them where necessary through a “heat break” or cycle designed to inactivate the disease, and carefully control growth and harvesting. When feeding sub-tropical shrimp a species such as the polychete Nereis Virens is a good candidate in that it grows in temperature latitudes only. An added security is if the wet ingredient, such as Nereis Virens, is farmed on land based ponds.
We have now devised an improved fish feed (which term is intended to include “bait” and the like), and method of producing same, in which at least some of the problems outlined above are at least alleviated.